1. Field of the Invention
The present invention relates to the field of manufacturing liquid crystal display devices, and in particular to a method for monitoring a contact hole etching process of a TFT substrate.
2. The Related Arts
Liquid crystal displays (LCDs) have numerous advantages, such as thin device body, less power consumption, and being free of radiation, and is thus widely used. Most of the flat panel display devices available in the market are backlighting liquid crystal displays, which comprise an enclosure, a liquid crystal panel arranged inside the enclosure, and a backlight module arranged inside the enclosure. The operation principle of the liquid crystal panel is that liquid crystal molecules are arranged between two parallel glass substrates and a plurality of fine vertical and horizontal wires is set between the two glass substrate, whereby electricity is selectively applied to cause change of the orientation of the liquid crystal molecules in order to refract out the light from a backlight module for formation of an image.
A liquid crystal display panel is generally composed of a color filter (CF) substrate, a thin-film transistor (TFT) substrate, liquid crystal (LC) interposed between the CF substrate and the TFT substrate, and a sealant. A general manufacturing process comprises a front stage of array process (including thin film, yellow light, etching, and film stripping), an intermediate stage of cell process (including bonding TFT substrate and the CF substrate), and a rear stage of assembling process (including mounting drive ICs and printed circuit board). The front stage of array process generally makes the TFT substrate for controlling the movement of liquid crystal molecules. The intermediate stage of cell process generally introduces liquid crystal between the TFT substrate and the CF substrate. The rear stage of assembling process generally mounts the drive ICs and combining the printed circuit board to effect driving the liquid crystal molecules to rotate for displaying images.
The TFT substrate generally comprises a glass substrate and TFTs formed on the glass substrate. To form the TFTs, insulation layers on a gate metal layer and source/drain metal layers must be removed through etching. However, since the insulation layers on the gate metal and the source and source/drain metal are of different thicknesses, end point detection is hard to implement in the etching machines in an etching process.
Furthermore, to effect electrical connection, a contact hole must be formed through etching an insulation layer in order to expose a source electrode. The formation of the contact hole is generally done in two ways. The first one is that formation is made by removing a drain insulation layer (PVX) and gate insulation layer with dry etching, where the source electrode of such a structure is generally made of Al/Mo; and the second one is that formation is made by removing a drain insulation layer (PVX) with dry etching, where the source electrode of such a structure is generally made of Mo/Al/Mo. Taking a TFT substrate of a 32-inch liquid crystal panel available from China Star Optoelectronics Technology (CSOT) of China as an example, a description of the thickness of each layer of the two structures will be given. For the first structure, the source electrode is made of Al/Mo, where the Al layer has a thickness of 3900 Å, the Mo layer has a thickness of 600 Å, a source/drain insulation layer (formed of SiNx layer) has a thickness of 2000 Å, and a gate insulation layer (formed of SiNx layer) has a thickness of 4000 Å; for the second structure, the Mo layer, the Al layer, and the Mo layer (from top down) of the source electrode respectively have thicknesses of 350 Å, 3000 Å, and 100 Å and the source/drain insulation layer (formed of SiNx layer) has a thickness of 2000 Å
A transparent conductive layer (ITO) is formed in the contact hole formed in the above process and etching is applied to form a via hole so as to achieve electrical connection between the source electrode and a pixel electrode. In the conventional etching process, a nano machine is used to inspect the thickness of a film to be etched and an etching depth is determined according to the thickness. However, the conventional nano machine has a limited range of inspection, whereby precise inspection cannot be made for a film having a thickness less than 300 Å. In etching a via hole, over etching will result in poor taping of ITO and easy wire breaking, and thus leading to abnormality of the thin-film transistor.